\section{THE ENGINE}

The engine used was an O.S. MAX .61 FX glowplug two-stroke piston engine widely used in RC airplane models. This model was chosen due to availability, its small dimensions and the low costs involved in its operation. This engine has one cylinder with a piston attached to the propeller shaft. It has also a throttle lever that controls the carburetor's valve opening. A glowplug positioned at the top of the cylinder's head provoques the engine ignition and is kept continuously glowing by the heat that remains inside the combustion chamber after each ignition. The fuel used during the experiments was a commercial type, containing mainly methanol with 10\% Nitromethane. The propeller used was the two-bladed APC 13x4. More detailed information can be found at \cite{motor_os}.